/// <summary>
/// Internal method to add an entity to the entity manager and register it with all
/// associated systems. This executes the add immediately.
/// </summary>
/// <param name="toAdd">The entity to add.</param>
private void InternalAddEntity(RuntimeEntity toAdd)
{
toAdd.GameEngine = this;
// notify listeners that we both added and created the entity
Log <GameEngine> .Info("Submitting internal EntityAddedEvent for " + toAdd);
EventNotifier.Submit(EntityAddedEvent.Create(toAdd));
EventNotifier.Submit(ShowEntityEvent.Create(toAdd));
// add it to the entity index
_entityIndex.AddEntity(toAdd);
// register listeners
toAdd.ModificationNotifier.Listener += OnEntityModified;
toAdd.DataStateChangeNotifier.Listener += OnEntityDataStateChanged;
// notify ourselves of data state changes so that it the entity is pushed to systems
toAdd.DataStateChangeNotifier.Notify();
// ensure it contains metadata for our keys
toAdd.Metadata.UnorderedListMetadata[_entityUnorderedListMetadataKey] = new UnorderedListMetadata();
// add it our list of entities
_entities.Add(toAdd, GetEntitiesListFromMetadata(toAdd));
}